1. Field of the Invention
This invention relates to heat-sealable edible films which can be used as sealing and packaging materials for dried foods, oily foods and the like, as well as processes for producing such films.
2. Description of the Prior Art
Generally, the powdered soup, flavoring oil, dried vegetables and other ingredients of precooked noodles and cup noodles are packaged to maintain their qualities and forms. The packaging materials used for this purpose include, for example, aluminum-polyethylene laminate, cellophane-polyethylene laminate and various plastic films.
In the case of cup noodles, dried vegetables and other ingredients may be added in an unpackaged state.
However, where powdered soup, flavoring oil, dried vegetables and the like are added in a packaged state, the packages must be torn to remove the contents prior to cooking. This is not only troublesome, but also has the disadvantage that the contents tend to be spilled at the time of tearing the packages, especially when they are in powder or liquid form.
Where such contents are added in an unpackaged state, this is disadvantageous, not only in that their flavors are lost easily and it is difficult to maintain their qualities, but also in that the maintenance of their forms is interfered with. Specifically, when cup noodles are shaken during transportation or handling, the ingredients and the like tend to migrate to the bottom of the cup. As a result, the consumer cannot recognize the presence of ingredients on removal of the cover.
One solution to these problems is to package such contents with an edible film. Thus, their qualities and forms can be maintained during transportation and storage. If the packaging material is soluble in hot water, the package can be dissolved simply by pouring hot water over it, thus making it unnecessary to tear the package. If not, the packaging material can be eaten together with the contents. Accordingly, it is highly desirable to package the contents with such a material.
Such a material must have sufficient film strength so that, during packaging or handling, the package may not be torn to release its contents. Moreover, it is desired from the viewpoint of packaging operation that such a material be heat-sealable. However, conventionally known edible films, for the most part, consist essentially of a water-soluble polysaccharide or a water-soluble protein. These films have excellent edibility and oxygen barrier properties, but fail to exhibit adequate heat sealability. Specifically, some of them cannot be heat-sealed under ordinary heat-sealing conditions, and some of them can be heat-sealed, but fail to achieve sufficient heat-seal strength. If the heat-sealing conditions are made severer to improve heat-seal strength, the film may undergo shrinkage or breakage.
In order to improve the heat sealability of edible films and thereby overcome the above-described disadvantages, a number of methods have been proposed. They include the method of forming a film from an intimate blend of amylose, an alkali metal salt of casein, and a low-molecular-weight plasticizer (Japanese Patent Laid-Open No. 112533/'76); the method of dipping a collagen film in, or coating it with, a mixture of gelatin or glue and a plasticizer (Japanese Patent Laid-Open No. 11280/'77); the method of forming a film by laminating a polysaccharide with gum arabic, pullulan, starch or gelatin (Japanese Patent Laid-Open No. 76336/'85); and the method of incorporating a solid fat in an edible film (Japanese Patent Laid-Open No. 59855/'88).
However, the films formed from an intimate blend of amylose, an alkali metal salt of casein, and a low-molecular-weight plasticizer, the films formed by laminating a polysaccharide with gum arabic, pullulan or starch, and the edible films having a solid fat incorporated therein still fail to exhibit adequate heat sealability. The films formed by laminating a collagen film or a polysaccharide with gelatin show a marked improvement in heat-seal strength, but have the disadvantage that the presence of gelatin in the surface layer causes severe blocking of films and this makes it difficult to handle the films.
Thus, there is a strong demand for an edible film having excellent heat sealability and blocking resistance.